• Journal of The Korean Astronomical Society
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• v.44 no.1
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• pp.1-11
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• 2011

A sample of 145 JHK-2MASS observations of NGC open star clusters is studied, of which 132 have never been studied before. Twelve are classified as non-open clusters and 13 are re-estimated self-consistently, after applying the same methods in order to compare and calibrate our reduction procedures. The fundamental and structural parameters of the 120 new open clusters studied here are derived using color-magnitude diagrams of JHK Near-IR photometry with the fitting of solar metallicity isochrones. We provide here, for the first time, a catalog of the main parameters for these 120 open clusters, namely, diameter, distance, reddening and age.

• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.21.4-22
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• 2011

IVS (International VLBI Service for Geodesy and Astrometry) 통합분석센터는 개별 IVS 분석센터의 산출물을 통합하고 그 결과물을 IERS (International Earth Rotation and Reference Systems Service)에 제공하여 국제 지구기준좌표계를 구축하고 지구회전파라미터를 결정하는데 핵심적인 역할을 한다. 한국천문연구원(KASI)은 2008년 10월 IVS 통합분석센터로 선정되어 현재 통합 분석 시스템을 구축하고 있다. 정규운영에 앞서 통합용 분석 소프트웨어를 정비하고, KASI 통합분석센터의 통합해를 타 IVS 통합분석센터 통합해와 비교 검증하는 것은 필수적이다. 이 연구에서는 통합분석처리를 위해서 GPS 자료처리 소프트웨어인 Bernese 5.0을 IVS 산출물 형식에 맞추어 수정 보완한 후 활용한다. 이 발표에서는 1984년부터 현재까지의 IVS 분석센터의 장기간 산출물을 수집하고 Bernese 5.0을 이용하여 지구회전파라미터(X-극, Y-극, UT1-UTC와 각각의 시간변화율)의 통합해를 산출한 결과를 소개한다. 또한, 타 IVS 통합분석센터의 통합해와 비교 검증결과를 논한다.

• Journal of Astronomy and Space Sciences
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• v.29 no.1
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• pp.63-67
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• 2012

Observations with milliarsecond resolution using the Navy Optical Interferometer have been obtained for a number of stellar systems which include high-mass binaries, eclipsing binaries, and radio stars. These observations also reveal the previously unseen companions in single-lined spectroscopic binaries via directly measured flux ratios. We will present examples of published and ongoing research efforts of these systems to illustrate how an optical interferometer contributes to our knowledge of stars, their environment, and companions. These studies include a conclusive revealing of the previously unseen companion in the single-lined binary ${\Phi}$ Herculis, the direct determination of orbital parameters in the wide and close orbits of Algol, and revealing the orbit of ${\beta}$ Lyrae with spatially resolved images of the $H{\alpha}$ emission.

• Publications of The Korean Astronomical Society
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• v.16 no.1
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• pp.21-23
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• 2001

The DE405 ephemeride is introduced as TRAO solar ephemeris system to support the apparent coordinates of planets after 2000. The time delay between planets and observer has to be regarded to get the apparent position of planet. Some fast algorithms about time delay are suggested to reduce the computing time. The CSI method is applied to run these algorithms on any O/S including both real-time and run-time machine.

• Journal of The Korean Astronomical Society
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• v.49 no.1
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• pp.9-18
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• 2016

Euclid, which is primarily a dark-energy/cosmology mission, may have a microlensing component, consisting of perhaps four dedicated one-month campaigns aimed at the Galactic bulge. We show that such a program would yield excellent auxilliary science, including asteroseismology detections for about 100 000 giant stars, and detection of about 1000 Kuiper Belt Objects (KBOs), down to 2-2.5 mag below the observed break in the KBO luminosity function at I ∼ 26. For the 400 KBOs below the break, Euclid will measure accurate orbits, with fractional period errors ≲ 2.5%.

• Journal of The Korean Astronomical Society
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• v.47 no.6
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• pp.215-218
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• 2014

One-dimensional (1-D) microlens parallaxes can be combined with heliocentric lens-source relative proper motion measurements to derive the lens mass and distance, as suggested by Ghosh et al. (2004). Here I present the first mathematical anlysis of this procedure, which I show can be represented as a quadratic equation. Hence, it is formally subject to a two-fold degeneracy. I show that this degeneracy can be broken in many cases using the relatively crude 2-D parallax information that is often available for microlensing events. I also develop an explicit formula for the region of parameter space where it is more difficult to break this degeneracy. Although no mass/distance measurements have yet been made using this technique, it is likely to become quite common over the next decade.

• Journal of The Korean Astronomical Society
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• v.49 no.4
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• pp.123-126
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• 2016

Microlensing is generally thought to probe planetary systems only out to a few Einstein radii. Microlensing events generated by bound planets beyond about 10 Einstein radii generally do not yield any trace of their hosts, and so would be classified as free floating planets (FFPs). I show that it is already possible, using adaptive optics (AO), to constrain the presence of potential hosts to FFP candidates at separations comparable to the Oort Cloud. With next-generation telescopes, planets at Kuiper-Belt separations can be probed. Next generation telescopes will also permit routine vetting for all FFP candidates, simply by obtaining second epochs 4-8 years after the event. At present, the search for such hosts is restricted to within the "confusion limit" of θ_confus ∼ 0.25′′, but future WFIRST (Wide Field Infrared Survey Telescope) observations will allow one to probe beyond this confusion limit as well.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.60.1-60.1
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• 2011

We present the preliminary results of the pilot observations for the fringe survey at 43 GHz with the VLBI Exploration of Radio Astrometry (VERA). The main goals of the fringe survey are to establish a full list of phase calibrators for the VERA dual-beam astrometric observations, and for the KVN multi-frequency phase referencing observations. We performed two 24 hours experiments as a pilot observation to test the feasibility of the fringe survey. Each source from a list of 220 sources has been observed in one scan for 2 minutes. 67 sources were detected with the SNR threshold of 3.5. The correlated flux densities of the detected sources are presented in four ranges of projected baseline lengths.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.41.1-41.1
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• 2009

한국천문연구원은 2008년 10월 IVS(International VLBI Service for Geodesy and Astrometry) 통합분석센터로 선정되어 현재 정규운영을 위한 준비 작업을 진행하고 있다. IVS 통합분석센터는 개별 IVS 분석센터에서 산출한 산출물을 통합하여 개별 분석 센터 산출물의 품질을 검증하고 국제 지구기준좌표계 구성에 필요한 입력 데이터를 제공하는 기능을 한다. 이 연구에서는 IVS통합분석센터로서의 역할과 향후 IVS 통합분석센터의 운영계획에 대해 초점을 맞춘다. VLBI 산출물 통합을 위해 다른 IVS 통합분석센터와 차별화하여 GPS 자료처리 소프트웨어 Bernese 5.0에서 제공하는 정규방정식 단계 통합 프로그램인 ADDNEQ2를 활용할 계획이다. 이와 관련하여 VLBI 데이터 처리에 적합하도록 ADDNEQ2를 수정 보완한 사항과 수정된 ADDNEQ2로 통합한 예비 결과에 대해 집중적으로 논의한다. 이와 더불어 산출한 예비 결과를 각 개별 IVS 분석센터 산출물을 바탕으로 비교 검증한 결과를 소개한다.

• Journal of The Korean Astronomical Society
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• v.49 no.2
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• pp.53-57
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• 2016

We present an optical UBVRI photometric analysis of the poorly studied open star cluster IC 2156 using Sloan Digital Sky Survey data in order to estimate its astrophysical properties. We compare these with results from our previous studies that relied on the 2MASS JHK near-infrared photometry. The stellar density distributions and color-magnitude diagrams of the cluster are used to determine its geometrical structure, real radius, core and tidal radii, and its distance from the Sun, the Galactic plane, and the Galactic center. We also estimate, the age, color excesses, reddening-free distance modulus, membership, total mass, luminosity function, mass function, and relaxation time of the cluster.